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CVE-2026-56389 is an OS command injection vulnerability in GNU Bison affecting HTML report generation. When Bison is invoked with HTML output enabled, a grammar file can define the configuration variable used for the XML-to-HTML transformation step. Specifically, the grammar-defined setting for the transformation executable is accepted without restriction and passed directly to execvp(), allowing attacker-controlled selection of the program to be executed. As a result, processing an attacker-supplied grammar with HTML report generation can trigger execution of an arbitrary program under the privileges of the Bison process. GNU Bison 3.8.2 was tested and confirmed vulnerable; other versions may also be affected, but a complete vulnerable version range is not currently available.
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A reported vulnerability affecting GNU Bison software.
An OS command injection vulnerability in GNU Bison's HTML report generation that allows attacker-provided grammar files to trigger arbitrary program execution.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.